Surface vehicles with venturi attachment

ABSTRACT

An automobile or other surface vehicle having the underside thereof formed so as to define a venturi to thereby reduce the tendency of the vehicle to lift from the ground during movement; an attachment for fitting to a vehicle to define such a venturi.

United States Patent [1 1 Oxlade Dec. 4, 1973 SURFACE VEHICLES WITHVENTURI ATTACHMENT [76] Inventor: Kenneth David Oxlade, Lot 3, KneesRd., Park Orchards, 31 14 Australia [22] Filed: Feb. 14, 1972 [21] Appl.N0.: 225,905

560,594 4/1957 Italy 296/1 S 1,336,673 7/1963 France 296/1 S OTHERPUBLICATIONS The Automobile Engineer, September 1928, Page 330.

Primary Examiner-Leo Friaglia Assistant Examiner-Leslie J. PapemerAtt0rney-D. Bruce Prout et a1.

[57 ABSTRACT An automobile or other surface vehicle having the undersidethereof formed so as to define a venturi to thereby reduce the tendencyof the vehicle to lift from the ground during movement; an attachmentfor fitting to a vehicle to define such a venturi.

6 Claims, 7 Drawing Figures PATENTEUUEB 41% 3,776,587

SURFACE VEHICLES WITH VENTURI ATTACHMENT BACKGROUND OF THE INVENTION i.Field of the Invention This invention relates to surface vehiclesincluding self-propelled vehicles such as automobiles, and vehicleswhich are not self-propelled such as trailers and caravans.

ii. Description of the Prior Art It is well known that surface vehicles,such as'automobiles, travelling at high speeds tend to lift from theground due to aerodynamic lift forces generated by air flowing over thevehicle as it moves. The lift is generated in a manner analogous to thegeneration of lift by an aircraft wing, the effective lifting forceacting up wardly and slightly rearwardly at approximately the windscreenposition in most automoblies. In addition to the lift force generated bythis means, there is also a further force acting to lift the forward endof many vehicles, this being due to the torque applied by the drivingwheels. That is to say, there is a tendency for the whole of the body ofthe vehicle to rotate about the rear axle in reaction to the drivingtorque of the wheels. There is thus also a tendency then for automobilesto assume an orientation, when moving, such that the body is upwardlyinclined towards the forward end thereof, the angle of inclinationincreasing, due to increasing driving torque, as speed increases.Because of this greater inclination or angle of attack, theeffectiveness of the body as an aerodynamic force generator increases sothat increase in speed of the vehicle results in a rapid rise in liftfirstly because of the proportionality of the force to the square of thespeed of the vehicle relative to the surrounding airmass, and secondlybecause of the increasing lift efficiency.

The result of the above effects, even if complete lifting does notoccur, is disadvantageous in that the posi-' tion of action of thelifting forces is such as to greatly decrease steering control bylessening the force holding the front wheels on the road surface;effective steering is of course dependent upon firm wheel to groundcontact. This difficulty is particularly apparent in racing vehicleswhere it has been found necessary to adopt measures for maintaining thevehicles on the road during racing andto ensure that sufficient frontwheel adherence is achieved. One common procedure is to add so-calledaerofoils" to the vehicles. These aerofoils comprise generally planarmembers disposed on the vehicle in a generally horizontal disposition.They are arranged to produce downward forces, that is forces in theopposite direction to the lifting forces normally produced byaeronautical aerofoils. In recent times, such devices have been usedquite extensively in professional racing, the aerofoils usually beingprovided one at the back of the driver and one to each side of thevehicle towards the front thereof.

The provision of aerofoils does to some extent assist in maintaining thevehicle on the road but they are not entirely satisfactory in use.

Firstly, it is necessary for them to be arranged at a negative angle ofattack to the airflow resulting from the forward movement of the vehicleif they are to be effective. That is to say, the leading edges must bedisposed at a lower point than the trailing edges. If the path of thevehicle were to be always horizontal, this angle would be maintained butin practice, since racing is often held over other than flat tracks, theangle of attack will vary due to pitching and, likewise, ordinarytransportation vehicles do not invariably travel on well surfaced flatroads. The angle of attack could also vary because of any other inducedforces acting on the vehicle. For example, the rearaerofoil is normallyplaced some distance above the vehicle in order to clear turbulence andthus, when the vehicle moves, the induced drag, being the horizontalcomponent of angled upward lift, created by movement produces a turningmoment acting about the axis of the rear wheels and constitutingcompound lifting of the front wheels.

It will be readily appreciated that because the normal angle ofincidence to the horizontal for the aerofoil is relatively small, itdoes not require very much movement of the vehicle to produce a changein attitude sufficient to displace the aerofoil such that the desiredangle of attack is not maintained, and variations in the downward forceproduced will result. For example, the angle of attack may reach a valuesuch that the aerofoil instead of producing downward forces on thevehicle may even produce some degree of upward lifting. Particularly inracing, drivers usually attempt to press the road-holding ability oftheir vehicles to the limit and the unforseeable variations in thisroad-holding ability caused by varying effectiveness of an aerofoil ismost undesirable, sometimes leading to disastrous consequences. Inrecent years greater negative angles have been used to offset some ofthese aspects but this causes greater drag forces.

Secondly, all aerofoils will induce drag forces which will vary inproportion to the square of the speed; it will be readily apparent thatdrag forces will often, at speed, be very considerable detracting fromthe performance of the vehicle. It may also be difiicult with particularvehicles to arrive at an aerofoil configuration which offers sufficienteffectiveness without causing excessive drag.

Another difficulty is that the area of an aerofoil which can be mountedon the vehicle, having due regard to the mechanical structure needed tomount it I and the amount of drag induced by such structure and theaerofoil itself, is limited and it will not always be possible toprovide a wholly satisfactory aerofoil on any particular vehicle. In anyevent, it is apparent that it is not very practicable to provideaerofoils of any size on automobiles for ordinary use, since they tendto obstruct clear vision of the driver and may present undesirableprojections which could seriously injure pedestrians.

Again, because the structure which mounts the aerofoil on the vehicle isgenerally made as light as possible there is a danger of the aerofoilbecoming dislodged and there have been several accounts of damage orinjury, in racing, caused to drivers or spectators as a result of beingstruck by aerofoils loosened from vehicles because of inadequatemounting. This also mitigates against the use of aerofoils on vehiclesintended for ordinary transportation purposes.

The invention provides improved means whereby a surface vehicle may bemore adequately constrained against tendencies to lift from the road tothereby avoid, at least to some extent, the above-mentioned dis- 5advantages associated with the use of aerofoils.

BRIEF SUMMARY OF THE INVENTION According to the invention there isprovided a surface vehicle characterised in that the under side thereofis constructed so as to define, in use of the vehicle, and between theunder side of the vehicle, and the surface upon which the vehicle istravelling, a venturi.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING The invention maybe better understood from the following description which is to be readin conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic side view of a vehicle constructed inaccordance with the invention;

FIG. 2 is a diagrammatic view of another vehicle constructed inaccordance with the invention;

FIG. 3 is a diagrammatic front view of the vehicle of FIG. 1 and that ofFIG. 2;

FIG. 4 is a fragmentary, partly diagrammatic view of v DETAILEDDESCRIPTION The vehicle 11 shown in FIG. 1 comprises a body 12, which inside elevation, is shaped generally in the form of an inverted wingsection of an aircraft. The forward end 12 of the vehicle is spaced somedistance above the ground line 13 and the forward underside portion 14is positioned so as to extend downwardly and rearwardly to a minimumdistance above the ground at a point 15 disposed towards the rear of thevehicle.

The distance of the point 15 above the ground is substantially less thanthe distance of the frontportion 12 from the ground. The underside rearportion of the vehicle 16 extends upwardly and rearwardly to the rearend 17 so that the rear end 17 is disposed somewhat at the same level asthe front portion 12. 1

The top 18 of the vehicle is substantially flat in this instanceexceptthat it is provided with a cockpit 19 for the driver. In use ofthe vehicle, and when it is driven forwardly, air flows underneath thevehicle and the under surface of the vehicle and the road surfacetogether define a venturi so that air flow about the point 15 takesplace at maximum speed and produces a local pressure reduction toproduce a downward force tending to cause the vehicle ,to remain uponthe. ground.

The surface 14 may be arranged at an angle of approximately 15 to thesurface 13 whilst the surface 16 may be arranged at an angle ofapproximately 795 thereto. However, other angles between 5 and 30, oreven as much as 45, for both surfaces will normally produce workableresults, with angles between 10 and 20 most satisfactory. The angle ofthe forward surface is preferably approximately twice the angle of therear surface.

In FIG. 2, the vehicle 21 has a generally flat upper surface 22 providedwith a cockpit 23. The lower surface 24 is curved so as to define twoportions 27, 28 disposed between the front end 29 and the rear end 31 ofthe vehicle. Portions 27, 28 are disposed relatively close to the groundso as to define two throats 33, 34

which, in use of the vehicle, produce low pressure areas under thevehicle in the same manner described in relation to FIG. 1. The lowpressure areas result in the production of forces which act downwardlyat these points.

It will be seen that the arrangement of the invention provides meanswhereby vehicles may be constructed in a manner such that they tend, inmotion, to generate forces which keep them upon the ground. Byappropriate shaping of the vehicle underside the centres of action ofthese forces may be arranged at any desired positions on the vehicle.

The height of the underside of the vehicle across the transverse widththereof is preferably substantially constant as is shown in FIG. 3, thatis to say, with the centre longitudinally extending portions 36 thereofdisposed substantially the same height above the road surface 37 as theouter longitudinal portions 37, 38. In some cases, it may be desirableto make the underside concave in transverse section.

In many cases, it is desirable to arrange the point of maximum downwardforce generation to coincide with the front end of the vehicle in orderto act against the effect of upward lift as previously described.

Again, the point of maximum downward force may be arranged near the rearwheels to improve rear wheel grip and prevent wheel spin duringacceleration.

FIGS. 4 and 5 show a vehicle 51 fitted with an attachment 52 which issecured to the underside of the vehicle between the front wheels 54 and56 thereof.

Attachment 52 is formed of fibreglass or other relatively rigid materialand presents a lower surface 53 which is flat in transversecross-section (FIG. 5) but which has a downwardly curved portion 53aextending from a transverse leading edge 57, the portion 53a mergingwith a rear portion 53b which extends upwardly in the rearward directionof the surface 53 to a rear edge 58. The forward portion 530 of surface53 extends downwardly at an angle of approximately 20 to the horizontalwhilst the rear portion 53b extends upwardly at'an angle ofapproximately 10. The 'attachment has upwardly extending side flanges59, 61 and upstanding front and rear flanges 62, 63. The rear flange 63is secured at a point, intermediate its length, to a downwardlyextending bracket 66 which extends below the chassis 64 of the vehicle.Likewise, the forward flange 62 is secured to chassis 64 by means ofabracket 67 on the underside of the vehicle.

The attachment 52 operates to produce a downward holding force in thesame way as the force that is produced by the shaping of the undersideof the vehicles of FIGS. 1 and 2. Edges 59, 61 assist in the maintainingof the pressure differential between upper and lower sides of theattachment to improve the efficiency of operation.

FIG. 6 shows an alternative method of mounting the attachment 52. Inthis case, the attachment 52 is secured to the chassis 64 by means ofpivot pins 71 which extend through the brackets 66 and 67 and enter thefront and rear flanges 62, 63. The axes of the pins 71 are coincidentand extend generally longitudinally of the vehicle so that theattachment is pivotal about the common axis of the pins. The attachmentis further interconnected, by means of a pair of link structures 72 and73, to the chassis. These each comprise pairs of links 72a, 72b and 73a,73b respectively. The links 72a and 73a are pivotally connected at upperends to the underside of the chassis 64 for pivotal movement in a commonplane transverse to the vehicle and intermediate the length ofattachment 52 whilst the links 72b, 73b are pivotally connected at lowerends to opposite sides of the attachment for pivotal movement in thesame plane. The free ends of the respective pairs of links 72a, 72b and73 a, 73b are pivotally connected together by means of pins 720 and 730respectively. The pivot pins 720, 730 preferably provide mountings forweights (not shown) although the weight of the links and pins may insome cases be sufficient to permit operation in the manner hereinbeforedescribed without the presence of such weights. By suitable selection ofthe weights or links and/or by the application of suitable resilientbiasing means, the link structures 72 and 73 are arranged to be normallyin the condition shown in FIG. 6, that is with the links pivotedoutwardly of the pivot points on the chassis with the underside ofattachment 52 maintained substantially parallel to the surface 81 onwhich the vehicle travels.

FIG. 7 illustrates the device secured as indicated in FIG. 6 when thevehicle is executing a left hand turn. It will be observed that, duringthis turn, the chassis 64 is tilted so that the right hand side is lowerthan the left hand side and there is an acceleration force directed tothe right in FIG. 7 which acts upon the weights and pins 720 to causeright hand structure 72 to compress vertically that is to say theoutward accelerative force on the weights on pins 720 causes the pins tobe moved in the direction of the acceleration force thereby decreasingthe obtuse angle between the two links 72a, 72b, and shortening thedistance between the right hand underside of the vehicle and theattachment 52.

Likewise, the acceleration force acting upon link structure 73 operatesto lengthen this by moving the.

pivot pin 73c inwardly as shown in FIG. 7, thereby increasing thedistance between the left hand underside of the chassis and theattachment 52. The effect of the alteration in lengths of the linkstructures 72, 73 is to pivot the attachment 52 about its longitudinalpivot axis in such a manner as to at least-substantially preserve theparallel relationship between the underside of the attachment 52 andsurface'8l, despite the rolling movement of the vehicle chassis. Thus,the effect on the attachment during turning is not 'altered to such anextent as would occur if it were fixed to the chassis and was therebypermitted to assume a transverse inclination to the surface 81. Theresult of this is to maintain the downward direction of the forcegenerated by the attachment.

It will be appreciated that when the vehicle 51 is in motion, the roadsurface will inevitably cause the vehicle to pitch and the forwardportion of the vehicle is thereby forced towards the road. During suchdownward pitching the attachment S2 is moved closer to the road surface,thus increasing the venturi effect produced thereby and thus alsoincreasing the downward force generated by the attachment to retard, tosome extent, the return movement of the front portion of the car. Thusthe additional force generated acts in a manner tending to correct anddampen the sometimes violent and rather unsafe return of the frontportion which would otherwise be produced by the car springs. Thus,lightening of the steering control which would otherwise occur isminimised.

The device when affixed as shown in FIGS. 4 and 5 operates to assiststeering during turning of the vehicle on flat or banked turns and toreduce the tendency of the vehicle to steer down a slope which is beingtraversed laterally. For example, with automobiles having front wheelssteerable, there is normally a tendency for the vehicle to castor down aslope which is inclined laterally of the vehicle. This tendency tocastor down transverse slopes arises because there is a turning momentwhich, in plan view of the vehicle, acts sidewardly through the centreof gravity of the vehicle, about the rear wheels, the moment beingproportional to the resolved component of weight down the slope. Thelift force acts at right angles to the surface producing it, whenconsidered in the lateral sense. A vehicle on a transverse slop has moreweight placed on the downhill springs thereby tilting the vehicle but ofparallel laterally with the slope. The lift force then is no longer atright angles to the road surface. Thus it will be readily appreciatedthat the resolved component of lift force, which acts upwardly upon thevehicle and now at a down-slope angle, also operates to assist thismoment and a considerable force may need to be exerted by the driver tokeep the vehicle properly on course on a cambered road when it is atsome speed. Against this force, the attachment 52 when secured as shownin FIGS. 4 and 5 will generate an oppositely directed moment. This isdue to the fact that the vehicle body tends to tilt about itslongitudinal axis, owing to the resolved component of weight actingthereon, so that the side of the vehicle located on the downhill orinside of the projected turning circle due to castoring will be somewhatcloser to the road surface than the uphill or outer side and theattachment 52, being rigidly secured to the vehicle, will thereby assumea disposition such that it is further disposed on its outer longitudinaledge from the ground than it is at the longitudinal inner edge.

The negative lift force generated by the attachment 52 will, of course,act at right angles to the attachment so that there will thus be aresolved component of this force which is directed outwardly of theprojected tuming circle and this causes a turning moment about the rearwheels which is directed outwardly of the steering circle. A vehiclefitted withthe attachment 52' will thus, on cambered roads, have atendency towards selfsteering in that the attachment will generate amoment tending to restore the entation; g

During turning on a flat road surface or on a banked turn taken at aspeed greater than the correct" speed, the body of an automobile tendsto tilt outwardly on the turn rather than being balanced as on aproperly banked turn taken at the appropriate speed so that there willbe an acceleration force acting through the centre of gravity of thevehicle and directed outwardly of the turning circle thereby producing amoment tending to cause the front portion of the vehicle to moveoutwardly rather than inwardly of the turning circle. However, theoutward tilt also alters the orientation of the attachment 52 (if it isrigidly secured to the vehicle) so that there will be a resolvedcomponent of negative lift force produced by the attachment and directedinwardly of the 'tuming circle. Again, therefore, the attachment willproduce a correcting moment which is directed against the outwardlydirected moment acting upon the vehicle due to turning to thereby assistin the front wheels to a straight line oristeering of the vehicle.

During cross winds, some degree of tilting of the vehicle about itslongitudinal axis normally results and this will cause alteration oforientation of the attachment S2 to direct the negative lifting force ina direction such that there is a resolved component again tending tocorrect the effect of sideways vehicle castor due to the cross wind.

Furthermore, in wet weather the efficiency of operation of the device 52or of vehicles constructed in accordance with the invention will beimproved since it is well known that forces produced by venturi effectare dependent upon the density of the fluid medium and, in wet weather,the density will be increased due to increased moisture content in theair. This will be particularly apparent, of course, close to the roadsurface because of the greater proportion'of water vapour there present.

It will be appreciated that the described embodiments of the inventionhave been described merely by way of explanation. In particular,although the disposition of the attachment 52 in the embodiments ofFIGS. 4 to 7 is particularly advantageous it is not essential that thisdisposition be adopted. The arrangement could be such as to generatenegative lifting force at any desired location on the vehicle. Likewise,the upturned side edges 59,61 could be dispensed with if desired. Theunderside of the attachment may, if desired, be lengthwise corrugatedsomewhat to improve strength, although at some small loss of efficiency.The method of mounting may, of course, be varied from that shown. Theattachment could be secured at or adjacent the four corners thereof, orindeed,.in any manner which does not interfere with the flow under theattachment. In the case where pivotal mounting is required, one pivotpin 71 and associated bracket 66 or 67 could be omitted. For example,the rear bracket could be omitted and the attachment held at the rearmerely by the link structures 72, 73. The attachment could also besecured, directly or via a suitable linkage, to moving members of thevehicle suspension to achieve the required movement relative to thevehicle body. Again, although in the arrangement of FIGS. 6 and 7, theattachment 52 is arranged to rotate to maintain itself generallyparallel to the road surface during turning, it may be desirable in someinstances to atrange it such that it tilts to a considerable extent, tosecure direction of the generated negative lift force as desired. Thiscould be accomplished, for example, by orienting the link structuressuch that pins 720, 73c are disposed inwardly rather than outwardly asshown, and thus increasing the self steering tendency at a small loss towheel/road contact pressure, when applicable.

Means other than the link structures 72, 73 and the brackets may also beemployed to ensure desired movement of the attachment relative to thevehicle. For example, the mass of the attachment itself, if pivotallysuspended, will act as a pendulum and can be suitably interconnected tosecure a desired movement of the attachment during roll of the vehicle.

Whilst the surfaces 14 and 16 are somewhat curved when viewed from theside, as is shown in FIG. 4, they may be straight (that is of constantincline throughout their lengths). The straight configuration issomewhat less satisfactory in use, but may be simpler to manufacture. j

Whilst the invention is described primarily in relation to selfpropelled vehicles, it may, of course, equally be applied to towedvehicles such as caravans or trailers.

In all cases, the efficiency of the arrangement will of course dependupon the clearance between the lowermost part of the structure 52 andthe ground. This clearance is preferably of the order of 6" but, ifdesired, a suitable mechanism may be employed to allow variation of thisclearance, so as to allow it to be increased or decreased to provide forvarying performance requirements. For example, a journey anticipatedover winding roads may indicate a lower position for the device. Thus,greater influence, to control dangerous rolling by the vehicle, could beobtained by reducing clearance to 4".

Aside from the above variations, the configuration of the vehicles shownin FIGS. 1 and 2, or of the attachment of FIGS. 4 to 7, could be variedso that the underside is generally convex in transverse cross section.

I claim:

1. A surface vehicle having a body portion and means supporting the bodyportion for movement of the vehicle over a ground surface, said bodyportion having affixed thereto an attachment to assist in maintainingthe vehicle upon said surface, said attachment comprising a membersecured to the underside of the body portion and having a lower surfacewhich extends downwardly from a forward edge thereof to a lower portionthereof and thence upwardly to a rear edge whereby to define, betweenthe attachment and said surface, a venturi, said attachment beingsecured to the body portion for pivotal movement about a generallylongitudinal and intermediate axis, andactuating means being providedfor effecting tilting of the attachment about this axis and in theopposite sense to roll rotation of the vehicle body portion about itslongitudinal axis produced during turning of the vehicle means for saideffecting rotation comprising two pairs of links, one to either side ofthe vehicle, one link of each pair being pivotally connected to theunderside of the vehicle to opposed lateral sides thereof and the otherlink of each pair being connected pivotally at one end to the free endof the associated link and at the other end pivotally to the attachmentat the same lateral side thereof as the associated link is attached'tothe vehicle, said'pairs of links being pivotal in generallyitransverseplanes and .being urged so that the connecting points'between links ofeach pair are disposed outwardly of lines passing through the points ofconnection of the associated links to the vehicle and attachment.

2. A surface vehicle having a body portion and means supporting the bodyportion for movement of the vehicle over a ground surface, said bodyportion having affixed thereto an attachment to assist in maintainingthe vehicle upon said surface, said attachment comprising a membersecured to the underside of the body portion and having a lower surfacewhich extends downwardly from a forward edge thereof to a lower portionthereof and thence upwardly to a rear edge whereby to define, betweenthe attachment and said surface, a venturi, said attachment beingsecured to the body portion for pivotal movement about a generallylongitudinal and intermediate axis, and actuating means being providedfor effecting tilting of the attachment about this axis, and in the samesense as, but additional to, roll rotation of the vehicle body portionabout its longitudinal axis produced during turning of the vehicle, saidmeans for efi'ecting rotation comprising two pairs of links, one toeither side of the vehicle, one link of each pair being pivotallyconnected to the underside of the vehicle to opposed lateral sidesthereof and the other link of each pair being connected pivotally at oneend to the free end of the associated link and at the other endpivotally to the attachment at the same lateral side thereof as theassociated link is attached to the vehicle, said pairs of links beingpivotal in generally transverse planes and being urged so that theconnecting points between links of each pair are disposed inwardly oflines passing through the points of connection of the associated linksto the vehicle and attachment.

3. A surface vehicle having a body portion and means supporting the bodyportion for movement of the vehicle over a ground surface, said bodyportion having affixed thereto an attachment to assist in maintainingthe vehicle upon said surface, said attachment comprising a membersecured to the underside of the body portion and having a lower surfacewhich extends downwardly from a forward edge thereof to a lower portionthereof and thence upwardly to a rear edge whereby to define, betweenthe attachment and said surface, a venturi, said attachment beingpivotally secured at a forward portion thereof to the vehicle bodyportion and rearwardly secured to moving members of the vehiclesuspension mechanism thereby to cause rotation of the attachmentgenerally about the longitudinal axis of the vehicle during roll of thebody portion produced during turning of the vehicle.

4. A surface vehicle having a body portion and means supporting the bodyportion for movement over a ground surface, said body portion havingaffixed thereto an attachment to assist in maintaining the vehicle uponsaid surface, said attachment comprising a member secured to theunderside of the body portion and having a lower surface which extendsdownwardly from a forward edge thereof to a lower portion thereof andthence upwardly to a rear edge to define, between the attachment andsaid ground surface, a venturi, said attachment being secured to saidbody portion for pivotal movement about a generally longitudinal andintermediate axis, and actuating means being provided for effectingtilting of the attachment about this axis so as to control the directionof force resulting from the venturi.

5. A surface vehicle as claimed in claim 4 wherein said actuating meanscomprises means for effecting rotation additional to, and in the samesense as, roll rotation of the vehicle about its longitudinal axisproduced during turning of the vehicle.

6. A surface vehicle as claimed in claim 4 wherein the last-mentionedmeans comprises means for effecting rotation of the attachment in adirection opposite to roll rotation of the vehicle about itslongitudinal axis produced during turning of the vehicle.

1. A surface vehicle having a body portion and means supporting the bodyportion for movement of the vehicle over a ground surface, said bodyportion having affixed thereto an attachment to assist in maintainingthe vehicle upon said surface, said attachment comprising a membersecured to the underside of the body portion and having a lower surfacewhich extends downwardly from a forward edge thereof to a lower portionthereof and thence upwardly to a rear edge whereby to define, betweenthe attachment and said surface, a venturi, said attachment beingsecured to the body portion for pivotal movement about a generallylongitudinal and intermediate axis, and actuating means being providedfor effecting tilting of the attachment about this axis and in theopposite sense to roll rotation of the vehicle body portion about itslongitudinal axis produced during turning of the vehicle means for saideffecting rotation comprising two pairs of links, one to either side ofthe vehicle, one link of each pair being pivotally connected to theunderside of the vehicle to opposed lateral sides thereof and the otherlink of each pair being connected pivotally at one end to the free endof the associated link and at the other end pivotally to the attachmentat the same lateral side thereof as the associated link is attached tothe vehicle, said pairs of links being pivotal in generally transverseplanes and being urged so that the connecting points between links ofeach pair are disposed outwardly of lines passing through the points ofconnection of the associated links to the vehicle and attachment.
 2. Asurface vehicle having a body portion and means supporting the bodyportion for movement of the vehicle over a ground surfacE, said bodyportion having affixed thereto an attachment to assist in maintainingthe vehicle upon said surface, said attachment comprising a membersecured to the underside of the body portion and having a lower surfacewhich extends downwardly from a forward edge thereof to a lower portionthereof and thence upwardly to a rear edge whereby to define, betweenthe attachment and said surface, a venturi, said attachment beingsecured to the body portion for pivotal movement about a generallylongitudinal and intermediate axis, and actuating means being providedfor effecting tilting of the attachment about this axis, and in the samesense as, but additional to, roll rotation of the vehicle body portionabout its longitudinal axis produced during turning of the vehicle, saidmeans for effecting rotation comprising two pairs of links, one toeither side of the vehicle, one link of each pair being pivotallyconnected to the underside of the vehicle to opposed lateral sidesthereof and the other link of each pair being connected pivotally at oneend to the free end of the associated link and at the other endpivotally to the attachment at the same lateral side thereof as theassociated link is attached to the vehicle, said pairs of links beingpivotal in generally transverse planes and being urged so that theconnecting points between links of each pair are disposed inwardly oflines passing through the points of connection of the associated linksto the vehicle and attachment.
 3. A surface vehicle having a bodyportion and means supporting the body portion for movement of thevehicle over a ground surface, said body portion having affixed theretoan attachment to assist in maintaining the vehicle upon said surface,said attachment comprising a member secured to the underside of the bodyportion and having a lower surface which extends downwardly from aforward edge thereof to a lower portion thereof and thence upwardly to arear edge whereby to define, between the attachment and said surface, aventuri, said attachment being pivotally secured at a forward portionthereof to the vehicle body portion and rearwardly secured to movingmembers of the vehicle suspension mechanism thereby to cause rotation ofthe attachment generally about the longitudinal axis of the vehicleduring roll of the body portion produced during turning of the vehicle.4. A surface vehicle having a body portion and means supporting the bodyportion for movement over a ground surface, said body portion havingaffixed thereto an attachment to assist in maintaining the vehicle uponsaid surface, said attachment comprising a member secured to theunderside of the body portion and having a lower surface which extendsdownwardly from a forward edge thereof to a lower portion thereof andthence upwardly to a rear edge to define, between the attachment andsaid ground surface, a venturi, said attachment being secured to saidbody portion for pivotal movement about a generally longitudinal andintermediate axis, and actuating means being provided for effectingtilting of the attachment about this axis so as to control the directionof force resulting from the venturi.
 5. A surface vehicle as claimed inclaim 4 wherein said actuating means comprises means for effectingrotation additional to, and in the same sense as, roll rotation of thevehicle about its longitudinal axis produced during turning of thevehicle.
 6. A surface vehicle as claimed in claim 4 wherein thelast-mentioned means comprises means for effecting rotation of theattachment in a direction opposite to roll rotation of the vehicle aboutits longitudinal axis produced during turning of the vehicle.